The proposed project is a series of studies focused on the relationship between myocardial respiration, metabolism and function. The close interdependence of the sequence beginning with myocardial ischemia, altered cellular oxygen demand, decreased oxygen utilization and depressed left ventricular function has made the isolated study of each of these difficult. A membrane lung perfusion system has been developed in this laboratory that permits rigid control of each of the variables of oxygen delivery to an isolated, beating heart doing no external pressure or flow work. Emphasis will be focused on those parameters of oxygen delivery (arterial pH, blood flow and arterial gas tensions) which can be regulated during cardiopulmonary bypass. The perfusion technology will also permit an absolutely stable model for the delineation and characterization of a reversible and reproducible infarct zone. A fluorescence photographic technique for the evaluation of epicardial pyridine nucleotide redox potential has been developed in this laboratory and correlated with ventricular ischemia. Fluorescence photographs of totally and marginally ischemic tissue will be correlated with high resolution electrophysiological maps. These studies should define whether an ischemic "borderzone" exists. Subsequent of infarct and "borderzone" size will be directly relevant to intraoperative myocardial preservation and the medical therapy of myocardial infarction.